Glasses and glass-ceramics and products made therefrom

ABSTRACT

1. IN A RECUPERATOR MATRIX COMPRISING AN ASSEMBLY OF INTEGRALLY FUSED TUBES ARRANGED IN A PLURALITY OF LAYERS OF TUBES SUPERIMPOSED ONE ABOVE THE OTHER IN SUCCESSIVE PARALLEL PLANES, THE TUBES WITHIN EACH PLANE BEING ESSENTIALLY PARALLEL TO EACH OTHER AND TRANSVERSE TO THE TUBES IN ADJACENT LAYERS, THE TUBES IN EACH LAYER FORMING A SERIES OF LONGITUDINAL PARALLEL PASSAGEWAYS THROUGH THE MATRIX, WHEREIN THE WALLS OF SAID PASSAGEWAYS (1) HAVE ESSENTIALLY ZERO POROSITY, AND (2) CONSIST ESSENTIALLY OF AN INORGANIC CRYSTALLINE OXIDE CERAMIC MATERIAL, AND WHEREIN THE INNER DIAMETER OF SAID PASSAGEWAYS IS AT LEAST 3 TIMES THE WALL THICKNESS THROUGH PORTIONS OF SAID WALLS COMMON TO ADJACENT FUSED TUBES, WHEREIN THE OPEN FRONTAL OR CROSS-SECTIONAL AREA OF EACH FACE OF THE MATRIX CONTAINING PASSAGEWAYS IS AT LEAST 32 PERCENT OF THE CROSSSECTIONAL AREA ACROSS SUCH FACE, THE IMPROVEMENT WHEREBY SUCH RECUPERATOR MATRIX CAN WITHSTAND TEMPERATURES OF 1500*F. FOR AT LEAST 1000 HOURS AND SAID MATRIX WILL HAVE A DIMENSIONAL STABILITY OF LESS THAN 250 P.P.M. AND WILL RETAIN ITS STRENGTH, COMPRISING HAVING SAID INORGANIC CRYSTALLINE OXIDE CERAMIC MATERIAL OF SAID MATRIX CONSIST ESSENTIALLY OF THE GLASS-CERAMIC FORMED BY THERMALLY IN SITU CRYSTALLIZING A GLASS CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS:   INGREDIENTS: WEIGHT PERCENT SIO2 52-78.4 AL2O3 12.8-27.5 LI2O 2.4-7 ZNO 0.25-6.7 NUCLEATING AGENT 3-9   WHEREIN SAID NUCLEATING AGENT IS SELECTED FROM THE GROUP CONSISTING OF TIO2, ZRO2 AND A MIXTURE OF TIO2 AND ZRO2 AND WHEN SAID NUCLEATING AGENT IS TIO2, IT IS PRESENT IN AN AMOUNT OF AT LEAST 3.2 PERCENT AND WHEN SAID NUCLEATING AGENT IS ZRO2 OR THE MIXTURE, THE ZRO2 IS PRESENT IN AN AMOUNT NOT IN EXCESS OF 3% BY WEIGHT, WHEREIN THE   ZNO+LI2O/AL2O3   MOLAR RATIO IS $1, AND WHEREIN THE SIO2/AL2O3 MOLAR RATIO IS FROM 4 TO 9 AND (A) WHEN THE SIO2/AL2O3 MOLAR RATIO IS FROM 4 TO LESS THAN 5, THE LI2O/AL2O3 MOLAR RATIO IS FROM 0.55 TO 0.91, AND THE ZNO/LI2O MOLAR RATIO IS FROM 0.06 TO 0.5; (B) WHEN THE SIO2/AL2O3 MOLAR RATIO IS FROM 5 TO 8, THE LI2O/AL2O3 MOLAR RATIO IS FROM 0.55 TO 0.93, AND THE ZNO/LI2O MOLAR RATIO IS FROM 0.04 TO 0.5; (C) WHEN THE SIO2/AL2O3 MOLAR RATIO IS FROM MORE THAN 8 UP TO 9, THE LI2O/AL2O3 MOLAR RATIO IS FROM 0.8 TO 0.93, AND THE ZNO/LI2O MOLAR RATIO IS FROM 0.04 TO 0.5; AND (D) THE GLASS AND RESULTING GLASS-CERAMIC CONTAINS IN WEIGHT PERCENT NO MORE THAN 0.2 K2O, OR 0.2 NA2O, OR 0.2 (NA2O+K2O), SAID GLASS-CERAMIC HAVING A COEFFICIENT OF LINEAR THERMAL EXPANSION OF -12 TO +12X10**-7 (0700*C.).

J. L.. PLANcHocK ETAL 3,841,950

GLASSES AND GLASS-CERAMICS AND PRODUCTS MADETHEREFROM Filed Feb. 28', 1972 Oct. l5, 1974 United States Patent O 3,841,950 GLASSES AND GLASS-CERAMICS AND PRODUCTS MADE THEREFROM Jerry L. Planchock, Toledo, Daniel R. Stewart, Maumee, and Thomas W. Brock, Toledo, Ohio, assignors to Owens-Illinois, Inc.

Continuation-impart of abandoned application Ser. No. 146,664, May 25, 1971. This application Feb. 28, 1972, Ser. No. 229,959

Int. Cl. B32b 5/12 U.S. Cl. 161-55 6 Claims ABSTRACT OF THE DISCLOSURE Thermally crystallizable glasses and glass-ceramics having a narrow critical range of compositions coming within the SiO2'A1203-Li2O and SiO2'A12O3Li2O-ZI1O SYS- tems and glass-ceramic products made therefrom including heat exchangers, such as regenerators and recuperators used with gas turbine engines, thermal reactors and catalytic reactors for the gaseous exhausts of combustion engines, and other products which are dimensionally stable at temperatures of at least 1500 F. and above, have very low coeicients of thermal expansion, and have a modulus of rupture of at least about 10,000 p.s.i. which is retained when operating at temperatures of at least 1500 F., over an extended period of time.

This application is a continuation-impart of co-pending U.S. application Ser. No. 146,664, led May 25, 1971, now abandoned.

In U.S. patent application Ser. No. 30,859, filed Apr. 22, 1970, and in U.S. application Ser. No. 146,665, led May 25, 1971, both of which are assigned to Owens- Illinois, Inc., assignee of the present application (the disclosure of each of which is incorporated herein by reference and thus forms a part of this application), there are disclosed several embodiments of heat exchangers, namely recuperators and regenerators for use with gas turbine engines for various automotive vehicles, including automobiles, trucks, busses, and the like, together with a full disclosure as to how to make such heat exchangers.

In each embodiment of the disclosures, the regenerative heat yexchanger comprises a matrix of integrally fused tubes forming a series of smooth longitudinal parallel passageways therethrough, wherein the walls defining the passageways are nonporous and consist essentially of an inorganic crystalline oxide ceramic material having an average lineal coeicient of thermal expansion of about -12 to +12 10'7/ C. (0-300 C.). The walls of the passageways also have a maximum thickness of about 0.03 to 0.002 inches through portions of such walls common to adjacent fused tubes. The ratio of the diameter of the passageways to the aforementioned thickness is at least 3 and the matrix has an open frontal area of at least 60%. Furthermore, the matrix walls have a thermal conductivity at 400 C. of less than 0.01 cal./cm./sec./ cmr'i/ C.

In the aforementioned U.S. application Ser. No. 30,859 and in the later filed application Ser. No. 146,665 which is a continuation-in-part of Ser. No. 30,859, there is disclosed a recuperator comprising a matrix comprising an assembly of integrally fused tubes arranged in a plurality of layers of tubes superimposed one above the other in successive parallel planes, the tubes within each plane being essentially parallel to each other and transverse to the tubes in adjacent layers, the tubes in each layer forming a series of longitudinal parallel passageways through the matrix. The composition and size of the tubes is substantially the same as that of the aforementioned regenerator tubes. Because of the arrangement of the layers of tubes in the recuperator, the open frontal or crosssectional area of each face of the matrix containing pas- 3,841,950 Patented Oct. 15, 1974 sageways is at least 32% of the cross-sectional area across each face.

-In U.S. patent application Ser. No. 127,127, filed Mar. 23, 1971, in the names of Andrew W. Zmuda and Yu K. Pei and entitled Exhaust Reactor for Combustion Engine (also assigned to the common assignee) the disclosure of which is also incorporated herein and forms a part of this application, there is disclosed an integral monolithic exhaust reactor for a combustion engine including a rst reaction zone comprising an elongated tube for receiving the flow of hot glass effluents from a combustion engine. A matrix comprising a plurality of parallel tubes extends longitudinally of and is disposed about the first tubular reaction zone and is bonded thereto. The parallel tubes are bonded together in the matrix and form a rigid support for the elongated tube. A plurality of the matrix tubes disposed about the elongated tube have open passageways which are in communication with the elongated tube and receive the ow of gas effluents therefrom. These matrix tubes dene a second reaction zone for the gas effluents and connect with outlet means to permit passage of gas therefrom.

During their operation, the regenerators, recup-craters, and exhaust reactors described in the aforementioned pending patent application are subjected to extremely high temperatures of about 1500 F. and more for extended periods of time. When the various components of such devices are formed of an inorganic `crystalline oxide ceramic material, such material must have thermal stability to withstand such high temperatures, i.e., its coefficient of thermal expansion, its modulus of rupture, its structural dimensions, and other properties must not change to any appreciable extent upon exposure to such high temperatures over extended periods of time.

The coeicient of thermal expansion must be low so that any rapid heating or cooling of the ceramic material components will not cause any build-up of thermal stresses and result in breakage of the component.

The modulus of rupture must be high so that such components can withstand the wear and tear inherent in normal operations of the gas turbines and automotive vehicles. Such strength must be maintained at the high temperatures of at least 1500 F. to which such components are normally subjected.

Heat exchangers, such as regenerators and recuperators used in gas turbine engines for trucks, operate at temperatures as high as 1500 F. and must be able to withstand this temperature for at least 1000 to 2000 hours without shattering during the operation of the truck. Automobile turbine heat exchangers will operate at temperatures as high as 1900" F., While catalytic and thermal reactors which ensure substantially total combustion of exhaust gas efuents of internal combustion engines will be subjected to temperatures of about 1000-1900 F. Thus, all components of these devices must retain their strengths while being subjected to these temperatures over extended periods of time and, most importantly, must retain their thermal stability during operation, particularly dimensional stability. Expansion of less than 250 parts per million when exposed to temperatures of at least 1500 F. for a period of 2000 hours should be a property of any glass-ceramic component utilized in these heat exchangers and reactors, and preferably such expansion should be less than p.p.m. with, of course, the ideal being an expansion of 50 p.p.m. or less at these temperatures over these times.

It has not been found that certain thermally crystallizable glasses having certain narrow, critical composition limits within the broad area of Li2O-Al2O3-Si02 and Li2O-Al2O3-SiO2-Zn0 systems, when shaped into specific structures and then thermally in situ crystallized to an at least partially crystalline ceramic (also referred to as glass-ceramic), impart to such structures excellent thermal stability at high temperatures of at least 1500 F. while simultaneously imparting a high modulus of rupture. Furthermore, such structures have a coeflicient of thermal expansion within the range of 12 to +12 107/ C. (-700 C.). Many of the compositions have a coefficient of thermal expansion of less than --3 to +3 X lO-'/ C. and some are within the range of 0.5 to +0.5`X -'7/ Cmmmmcm Thermally crystallizable glass compositions of the invention coming within the SiO2-Al2O3-Li20 system consist essentially of the following ingredients present within the indicated ranges, expressed in weight percent, and also within the indicated molar ratios.

wherein the nucleating agent is either 'I`i02 or a mixture of Ti02 with ZrOZ. Usually, in order to obtain the desired properties, the compositions will consist of 98-100 weight percent SiOz-i-AlzOS-l-LZO-i-the specified nucleating agents. When the SiO2/Al203 molar ratio is from 4 to less than 5, the U/A1203 molar ratio is from 0.75 to 0.97; when the SiO2/Al203 molar ratio is from 5 to 7.5, the M20/A1203 molar ratio is from 0.65 to 0.97; when the Si02/Al203 molar ratio is more than 7.5 and less than 9, then the U20/A1203 molar ratio is from 0.8 to 0.97; and when the Si02/Al203 molar ratio is more than 9 and up to 10, the M20/A1203 molar ratio is from 0.87 to 0.97. More usually, the weight percent ranges of Si02 and Al203 in these compositions are 62.8-80 SiOz and 12.7- 26.7 A1203.

When the nucleating agent is a mixture of TiOZ-l-ZrOg then the Zr02 should not exceed 3 and preferably should be less than 3% i.e. up to 2.8% by weight and preferably at least 0.5% by weight, and the total amount of Ti02 plus ZrOz is at least 3 weight percent up to about 9 weight percent.

While more than about 9 weight percent TiOg or total nncleating agent may be used, there is no advantage in using such large amounts because the properties of the resulting glass-ceramics are not improved. Further, raising the Ti02 levels has the result of raising the thermal expansion coeicient of the glass-ceramic. It is critical to have at least 3 weight percent nucleating agent in the composition. When less than 3 weight percent total nucleants are present, the nucleation rate is so slow that the heat treatment cycles are excessively long and the strength of the glass-ceramic which is formed is decreased. When ZrO2 is present in an amount of 3 Weight percent or more it raises the liquidus of the glass melt and makes more dilicult the processing of the glass into products.

Refining agents, such as antimony tri-oxide, arsenic oxide, or the like, may be present inthe composition in an amount up to about 0.5 weight percent if such ingredients are deemed necessary for iining the glasses.

In the preferred embodiment of the invention, the thermally crystallizable glass comes within the following composition ranges wherein the sole essential ingredients, ex-

pressed in weight percent, are as follows, and wherein the molar ratios are as indicated:

Ingredient: Weight percent SiOz 63-7 8.5 A1203 13.8-23 LizO 3.56.5 Nucleating agent 3-9 Composition number .m

1Q DIGO O mesmo wowowsog ses "ce om ma mangeurs?,

Molar*` ratio:

C on

edo'

CID O55 Representative compositions coming within the scope of the present invention are set forth in Table I.

Whenever the glass-ceramic falls outside the range of ingredients set forth above, either the coefficient of thermal expansion is too high or the dimensional stability at high temperatures, and/ or the strengths of such glass-ceramics during high temperature operations are poor. To show the criticality in the U20/A1203 molar ratio reference is made to Table II wherein several compositions of the invention having dilerent H2O/A1203 ratios were compared with two compositions which were outside the range of the invention because of lower ratios. All compositions were melted, drawn as 1A" rods from the melt, and the glass rods heated to form glass-ceramic rods.

The glass rods were heated to their nucleating temperature at a rate of 300 F. per hour, and held at that temperature for 8 hours. They were then heated to the nishing temperatures set forth in Table II and held there for two hours. All rods were then cooled at 25 F. per hour to 1500 F. then cooled to room temperature at the furnace rate of about 300 F. per hour. All compositions had a nucleating temperature of 1350 F. except Compositions 16 and 26 which had nucleating temperatures of 1375 F. and 1300 F., respectively.

The foregoing heat treatment schedule was used to form the glass-ceramic rods referred to in all subsequent tables of this application, and the nucleating temperatures of the particular compositions will lbe set forth in the discussions regarding each table.

The following batch materials were mixed and melted in a furnace to form the glass of Example 16:

The H2O/A1203 molar ratios of 1.05 in Composition 23 resulted in the glass-ceramics having very poor dimensional stability at 1500 F. The expansion of +490 parts per million after only hours at 1500 F. showed that with longer times the expansion would be considerably greater and the glass-ceramic would not be satisfactory where the product made therefrom would be subjected to temperatures of at least 1500 F. for extended periods of time. Composition 24 also was unacceptable since the glass-ceramic broke during the heat treatment. When the U/A1203 molar ratio was within the range of 0.95 t0 0.70, the resulting glass ceramic had good high temperature properties including good dimensional stability at 1900 F. However, when the molar ratio of U20/A1203 was as low as 0.6 and lower as in Compositions 25 and 26, the resulting glass-ceramics had very low strengths. The samples of Examples 25 were very weak at the intermediate heat treatment step of 1800 to 2000 iF. and were very unsatisfactory. Compositions of the invention, however, had modulus of rupture values in excess of 10,000 p.s.i. and are suitable for use at high temperatures over long periods of time because of these strengths. The glass-ceramic of Composition 26 had a coecient of thermal expansion of 18.2 107 (0-300" C.). Such compositions are unsuitable for the purposes of this invention.

Compositions 20, 22, and 29, which are representative of those coming within the scope of the present invention, were compared with other compositions falling outside of the invention because of too low a silica content and a resulting low SiO2/Al203 ratio. Again, the compositions Ingregiems: .1. Parts by Wlsgl were melted, glass rods of 1A diameter were drawn out Attv 2151 Ea 1016 therefrom and then heat treated according to the sched- Ti-tanOXumma 73 35 ule set forth in connection with Table II compositions Lithium z ic'ggt-e "1081 and the iinishing temperatures given in Table II'I. The Sodium antimonate 20'5 nucleating temperatures were 1250 F. for Composition .Lithium carbonate 488 28; 1300 F. for Compositions 22 and 27; and 1350u F. Lithium Chloride 47,8 40 for Compositions 20 and 29. Various properties of the Lithium nitrate 27.6 resulting glass-ceramlcs were then measured.

TABLE III Composition number 22 27 28 20 29 Ingrfiiinnts (moles) 2- so Hefltratmlenagenpfr. (tnne, lgs.) l 2,100@ 2,100(2) 2,100(2) 2,200@ 2,100(2) D lgfigri. -15(2,000) 298(100) 79(250) 1,900 F (nrs.) M d l f t .S.i.,room tern 11,200 6,10 13,800 11,300 Cgeiiiclirt ilhelrriiaillexpansion, orXiO+7 (0-700 C.) +6. 8 +5. 3 5. 9 +4. 2 7. 1

The sodium antimonate, lithium chloride and lithium nitrate are present as refining agents for the glass melt. The batch was melted at 2970 F. for a period of 23 hours and mechanically stirred during this time. From the disclosure of the batch of the foregoing example, those in the glass art can readily make the glasses coming within the present embodiment of the invention.

TABLE II Composition number 23 24 7 14 15 16 19 25 26 In redients moles g Li20 1. 05 1. 0 0. 95 0. 9 0.85 0. 8 0. 7 0. 6 0. 5 A1203-- 1 1 1 1 1 1 1 1 1 'O2 6 6 6 6 6 6 6 6 6 Heat treatment tem e, hrs.) p 2, 220 (2) 2, 100 (2) 2, 201)(2) 2, 200 (2) 2, 200(2) 2, 100(2) 2, 200(2) 2, 200(2) Dlllnensio'ial stabilityiz,

c ange n p.p.m., a

1,500 F. (time, hrs.)-..- +490(10) +27(100) +35(100) -13(250) M 1,900 F. (time, hrs.) -196(2,000) 104(2,000) -182(2,000) +205 (2, 000) +76(100) odulus of ru ture .s i room temp.)p p 14, 600 1l, 300 10, 500 10, 700 l1, 500 12, 200 4, 300 Coefficient 0f thermal expension X10H (0-700" C.) +3.8 +1.6 -l-LO -l-Ll +1.6 +1. 8 +8.8

*Samples broke. At LMO/A1203 molar ratios of 1, the resulting glass could not be heat treated to a glass-ceramic since the samples all broke during the heat treating steps.

pand considerably more after longer times at this high temperature, thus making it very unsatisfactory for purposes of this invention. As seen from Composition 28, a U20/A1203 molar ratio of 0.7 is too low when the S102/ A1203 ratio is 4.3 and results in a glass ceramic having very low strength values. However, with the same low 0.7Li2O/Al203 molar ratio, a good glass ceramic is obtained when the SO2/A1203 ratio is 5, as shown by Composition 20.

Composition 29, which has a lower U20/A1203 molar ratio than Composition 22, still produced a glass ceramic having a high modulus of rupture and a W expansion coelicient, comparable to that of Composition 22.

The effect of Liz() on compositions having a high SiO2/ A1203 ratio was ascertained and the results are set forth in Table IV. Again, each composition had its batch ingredi ents melted, and a rod having a 1A" diameter was drawn therefrom and heat treated according to' the nucleating and crystallization rates set forth above, using the finishing temperature set forth in Table IV. The nucleating temperature was l350 F. for Compositions 3, 30 and 31 and 1375 F. for Compositions 1 and 4.

As evident from the data in Table V, Na and K2O have a very detrimental elect on the dimensional stability at high temperatures of the compositions of the present invention. For example, Compositions 32 and 33 have a 0.95 :1:6 molar ratio of LiZO-AlgOs-SiOz and contain different levels of Na2O-l-K2O, namely 0.7 and 1.2 total weight percent, respectively. While Compositions 8, 11 and 12 are dimensionally unstable at 1900 F., they do have satisfactory stability at 1500 F. for 2000 hours and can be used in those devices wherein a temperature substantially over 1500 F. will not. be encountered during normal operation, such as in a regenerator for a gas turbine engine used for trucks.

To achieve good dimensional stability at 1500 F., the Na2O should not be present in an amount more than 0.5 Weight percent and the K2O should not be present in an amount of more than 0.5 Weight percent, nor should the combined Na2O+K2O exceed 0.5 Weight percent. To obtain good stability at temperatures of 1900 F. no more than about 0.25 percent NazO or K2O can be present, either by themselves or as a mixture.

Fe203 when present as an impurity in an amount of TABLE IV Composition number 4 3 1 y 30 31 Ingredients (moles):

S102--- s s 10 1o 10 Heat treatment, temp, F. (time, hrs.) 2. 10(1(2) 2,100@ 2, 101](2) 2, 101)(2) 2, 101)(2) Dimensional stability, parts per million (time, hrs.) at- Compositions 1, 3 and 4 exhibit acceptable high temperature properties. On the other hand, Compositions 35 and 31 are not suitable for the purpose of this invention less than 0.5 wel ht ercent has no detrimental effect on bec.ause of their high thermal expfmslon propelues and' the compositions gof tllle invention. However uoride ion their 10W strengths' Thys the 07h20/ A1203. ratio found which is known by the art to increase the strength of acceptable at (.)ther S102/ A4203 molar ratlos 1s unac' 40 glass-ceramic compositions when present in small ceptabk at a SOz/izos ratio of 10 Futher the glass' amounts adversely affects the ro erties of the comporaml of Composition 3.10 had a Cclengof thermal sitions df the present inventiolii. 1Composition 35 congggiliogfOgixalgoegggf gveglrgef tained 0.2 weight percent F and could not be heat treated o without the formation of surface scale because of the 0 300 C' ralige.' Bod? compositions are unsuitable for 45 crazing which took place. Composition 34 had very poor purposes of this. invention because of these very poor exdimensional stability, namely a Change of 750 p P m pansron properties. s

be of Vennon tile thermally Crystalilzaple glass compositions tion will, become evident from the further disclosure of must cfmslst of the three esenual Ingredients Sicz A1293 another embodiment of the invention Where it Will be and L12() plus .tile nucleaung agent) au faumg Within demonstrated that ZnO does not have a detrimental elect the. narrow critical ranges Se? forth above both .as to on dimensional stability at 1500 F but, instead makes wFlght percent of ach Ingredient an? to molar. mno? .of the glass-ceramic stronger. Fluoride, should be liept t0 D20/A1203 and S102/ A120?" Ingredients .and lmpumles less than 0.1 Weight percent and preferably is absent sgersqgtalgsma tlohkret which are It is critical in this first embodiment of the invention p n e p r a to have the crystallizable glass and the glass-ceramic con- L-S102-A1203 sist essentially solely of the three essential ingredients compositions cannot be tolerated above certain very plus dse nlcleamg agent coming Within. tile Weight minor levels and preferably should be omitted altogether '21g ul a. mtiar rmols( dened above' It 1S lm pratwe ffgg; fhgclgmgssitggsoffgeIgeswfnvglnfg-fhegf 6 while noiiis Sioutbopsesiu gli o a2, 2 an onte unensron staiityote glass-ceramic compositions is set forth in Table V. All of that 1t 1S almost lmposslble to make glass Wlthout some the glass ceramics were formed from glass rods which were then heat treated at 2100 F. for two hours.

TABLE V gomposition number- 7 s 12 11 32 33 9 1c 34 35 Lngredienlzs (wt. percent):

aan. l 0.45 0.1 Dimensional stability, parts per million (time: h'rs.) at- 0' 3 0' 2 sa .is 1 t +613 +301 s a +75 1:90a" s121000 nrs: a2 +330 +434 +987 .'IIIIIIIIII +i|ss :7g IIIIIIIIIIIII *Composition 35 was unsatisfactory sinceit crazed oni ts surface, no matter what heat treatment was used.

impurities unless only pure materials were used in the batch. This is not possible on any commercial scale because of the costs. However, care should be maintained in selecting batch materials for making the glasses to insure that impurities in the resulting glasses are kept to as low a figure as possible. It has been found that when petalite is used as a batch ingredient, for instance, that the resulting glass-ceramics do not have the desired properties of the glass-ceramics of the present invention. Accordingly, petalite cannot be used as a batch ingredient in making the glasses and glass-ceramics of the present invention.

In such other embodiment of the invention it has been found that thermally crystallizable glass compositions consisting essentially of SiOz, A1203, Li2O and ZnO, wherein each ingredient is within a narrow critical range and also within certain critical molar ratios, can be formed into articles which when heat treated to thermally in situ crystallize them to an at least partially crystalline ceramic, also referred to as a glass-ceramic, exhibit good thermal stability, good exural strengths and low coeicients of thermal expansion. The presence of the ZnO vastly improves the strengths of the glass-ceramics to almost double the strengths of the compositions of the first embodiment of the invention discussed above. Strengths within the range of about 13,000-20,000 p.s.i. and more can be readily obtained.

Such compositions coming within the scope of this second embodiment of the invention consist essentially of the following ingredients present Within the indicated weight percent ranges and also within the specific molar ratios:

wherein the ZnO -I-Li A1203 molar ratio is S1 and when the SiOz/AlzO'a molar ratio is from 4 to less than 5, then the U20/A1203 molar ratio is from 0.55-0.91 and the ZnO/Li2O molar ratio is from 0.06 to 0.5; when the SiO2/Al203 molar ratio is from 5 to 8, then the U20/A1203 molar ratio is from 0.55 to 0.93 and the ZnO/Li20 molar ratio is from 0.04 to 0.5; and when the SiO2/Al203 molar ratio is from more than 8 and up to 9, then the H2O/A1203 molar ratio is from 0.8 to 0.93 and the ZnO/LizO molar ratio is from 0.04 to 0.5. Usually, in order to obtain the desired properties, the compositions will consist of 98-100 weight percent SiO2+Al2O3|Li2OlZnO+the specified nucleating agents.

The nucleating agent can be TiO2, ZrO2 or a mixture of TiO2 and ZrO2. If TiO2 alone is used, it should be in an amount of at least 3.2 weight percent. If ZrO2 is used with TiOZ, it should not exceed 3% and preferably should be less than 3%, i.e. from about v0.5 to about 2.8 weight percent. In the latter event, suilicient TiOz must be present to at least give a total of 3 weight percent nucleating agent mixture in the composition.

Representative compositions coming within the scope of the second embodiment of the invention are set forth in Table VI.

TABLE Vl Composition number The LizO-ZnO-AlzOg-SiOg compositions of this embodiment of the invention have better heat treatment characteristics than the aforementioned Li2O-Al2O3-Si02 compositions of the invention. At heat treatment temperatures of 2000-2200 F., the latter compositions undergo a dimensional expansion which is caused by grain growth and the development of voids or pores at the grain boundaries. The change in length during heat treatment of Compositions 16 and 37 is shown in FIG. 1. Both compositions undergo an initial shrinkage and this shrinkage accompanics the crystallization of the high quartz solid solution phases in the temperature range of l350 F. to 1600D F. At temperatures between l600 F. and 2000 F., the high quartz phase undergoes a solid state transformation to the keatite solid solution phase. This phase change in Cornposition 37 is accompanied by a 0.3% lineal expansion at about 1725 F. At temperatures above 2000" F., Composition 16 expands by about 2.5% but Composition 37, which contains ZnO, does not change.

The behavior of these compositions at high temperatures gives the ZnO-containing compositions of the invention an advantage over the compositions of the invention which do not contain ZnO. With the latter compositions, the heating rates in the heat treatment cycles must be slowed down in temperature ranges where dimensional changes occur, particularly when an article such as a matrix or assembly for a regenerator, recuperator, thermal exhaust reactor and the like, is being heat treated to themally in situ crystallize it to form the integral monolithic glass ceramic structure. lf the product being heat treated has a temperature gradient, parts of it will tend to change dimensions before other of its parts and mechanical stress resulting in fracture will occur. Thus it takes about a week to heat treat and thus crystallize a product having a substantial thickness of several inches or more made from Composition 16 and less than two days to heat treat and crystallize the same product made from Composition 37.

Furthermore, it is easier to predict and control the dimensions of a product made from a glass composition which undergoes very small dimensional changes in the iinal stage of the heat treatment cycle as it becomes a glass-ceramic product.

Another important advantage of the ZnO-containing compositions of the present invention is that they are significantly stronger than the compositions of the invention which do not contain ZnO. The room temperature modulus of rupture of the former is at least 13,000 and is often 20,000 p.s.i. or higher as compared to approximately 10,000 p.s.i. for the latter.

NaZO, K2O, F2 and other impurities, When present in the ZnO-containing compositions of the present embodiment of the invention also adversely aiect the dimensional stability of the glass-ceramic formed therefrom. Thus, as little as 0.3 Weight percent Nag() causes poor dimensional stability of the glass-ceramic, namely an eX- pansion of |631 p.p.m. when held at 1500 F. for 250 hours for Composition 59A. NaZO-l-KZO in an amount of about 0.3 Weight percent also adversely effects the stability as does K2O per se when present in such an amount. Thus, an important and essential feature of these compositions is that the weight percent of Na20 and KZO, either alone or combined be no more than 0.2 weight percent. Fe2O3, when present as an impurity in an amount less than 0.5 weight percent, has substantially no eifect on the stability properties of the glass-ceramic. F, on the otherhand, even when present in an amount as low as 0.2 weight percent, imparted a 750 ppm. change in Composition 34 after 100 hours at 1500 F. See Table V, supra. Thus, uorine should be present in amounts less than 0.1 percent, and preferably not at all.

To show the effect of the U20/A1203 molar ratio on the properties of the compositions, ve glasses were melted, drawn as 1A: inch rods and heat treated in accordance with the schedule set forth above with respect to the Table Il compositions and where the finishing temperatures are set forth in the following Table VII. All compositions had a nucleating temperature of l350 F. except for Composition 60, which was 1300 F. Composition 37 was prepared from the following batch:

Ingredient: Parts by Weight Ottawa silica 3612 A-l0 alumino 888 Titanox 70.5 Sodium antimonate 20.5 Lithium carbonate 487 Lithium chloride 48 Lithium nitrate 28 Zinc oxide 70.6 Zinc zirconium silicate 176.5

The batch was melted at 2980 F. for twenty-two hours while being mechanically stirred. Other compositions coming within the scope of this embodiment of the invention were similarly made, except that the amounts of the ingredients varied accordingly. Those in the art will know how to make all of the compositions of the invention from the foregoing disclosure.

Dimensional stability and strengths of each glass-ceramic were then measured:

TABLE VII Composition number- 37 38 39 60 Ingredients (moles):

LisO 0.8 0. 7 0. 6 0. 4

SiOz 7. 0 6. 5 6. 5 6. 5

ZnO H .11 .1l .11 .11 Heat treatment, temp., F. (time, hrs.) 2, 10(1(2) 2, 200 (2) 2, 200(2) 2, 200(2) Dimensional stability, parts per million (time, hrs.) at- 1,500 F. (hrs.) 157(2, 000) 13. 1(25) 1640, 000) 48(500) 1,9oo F. (hrs.) 4700250) Modules of rupture (p.s.i., room temp.) 16, 100 16, 700 16, 600 14,100 Coelicient of thermal expansion, a 10+7 (tl-700 C.) 2. 7 1. 9 1. 5 35.8

*Hours Compositions 37, 38 and 39 have excellent stability after being subjected to the high temperatures for extended periods of time and also have high strengths. Composition 60 which has a low H2O/A1203 molar ratio has a very high coefficient of expansion which makes it completely unsatisfactory for purposes of the invention.

To show the elect of ZnO to the basic properties of the glass-ceramic, the following glass-ceramics were prepared from corresponding crystallizable glasses, drawn into 1A rods and heat treated in accordance with the schedule set forth above with respect to the Table II compositions. The inishing temperatures are set forth in Table VIII. The nucleation temperatures are as follows: 1250 F. for Compositions 40 and 41; 1300 F. for Composition 42 and l350 F. for the remaining four compositions.

Composition 64 could not be properly crystallized and was a very weak product having a modulus of rupture of 2000-3000 p.s.i. Composition 65 has a very low modulus of rupture and a high coeicient of thermal expansion, both over the -700" C. and the 0-300 C. ranges. When the SiOz/ A1203 molar ratio was 8, however, as in Compositions 55 and 57, the strengths of the glass ceramics tripled over that of Composition 65 while the expansion coecients became very low.

The elect resulting from too low a SiOZ level in the compositions is seen from Table X. While Compositions 51 and 54 have good high temperature properties, where the U20/A1203 ratio is as low as 0.6 with low SiO2 levels, the SiO2/Al203 should not be lower than 4, because of the very poor forming properties of the glass. Composition 66, on the other hand, did not crystallize and broke TABLE VIII Composition number 40 41 37 42 61 62 63 Ingredients (moles):

ZnO 0.25 0. 17 0. 11 0. 07 0. 04 0. 02 0.01 Molar ratio: ZnO/LMO O 0. 31 0. 21 0. 14 0. 09 0. 05 .025 25 Heat treatment, temp., F. (time, hrs.) 2, 100 (2) 2, 100(2) 2, 100(2) 2, 200 (2) 2, 100 (2) 2, 100 (2) 2, 100 (2) Drmenstronal stability, parts per million (time, hrs.) at

1,900 F. (hrs.) -119(1,000) +156(500) 147(250) Modulus of rupture (p.s.1., room temp.) 20, 100 13, 800 16, 100 15, 100 13, 400 10, 100 9, 900 Coeeient ol thermal expanslon, a +7 (0-700 C.) -2.7 -1. 0 +6 0 0. 1 -0. 6

-From the above table it can be seen that Compositions 37, 40, 41, 42 and 61, which have a SiO2/Al203 ratio of 0.8 and less have a molar ratio of ZnO/Li within the range of 0.04 to 0.5 and thus the presence of the ZnO affects and increases the modulus of rupture properties of the glass-ceramics. However, when the ZnO/Li-2O molar ratio is outside of the range of 0.04 to 0.5, the resulting glass ceramics, while they have good high temperature properties, are no better than glass-ceramic compositions having no ZnO. Thus, in order to achieve the increase in modulus of rupture, the amount of ZnO must come within the critical ranges set forth above, both as to weight percent and as to molar ratios.

The most usual compositions of this embodiment of the invention are as set forth hereinbefore but with the Weight percent ranges of SiO2, A1203, Li20 and ZnO in the following narrow ranges:

Ingredient: Weight percent SiO2 S82-78.4 A1203 13.7-26.5 Li2O 3.2- 6.9 ZnO 0.3- 6.5

TABLE IX Composition number 64 65 55 57 Ingredient-s (moles):

Li2O 0.6 0.8 0.8 0.8 1 1 l 1 10 10 8 8 ZuO 0.11 0.11 0.11 0.056 Heat treatment, temp hrs. 2, 100(2) 2, 200(2) 2, 200(2) Dimensional stability, parts per million (time, hrs.) at- 1,500 F +4905) 20(10) 1,900 F +2300) Modulus of rupture (p temp.) 7, 000 21, 000 20, 800 Coefficient of thermal expansion:

a l0+7 (0-700 C.) +11 4. 6 4. 0 0000+7 (0-300 C.) +31 1 Low strength.

during the heat treatment. The nucleation temperature for Compositions 51 and 54 was 135 0 F.

Dimensional stability, parts per millioio (ltime, hrs at- 1,900 F 88(250) Modulus of rupture (p.s.i., room temp. 13, 400 16, 000 Coefficient of thermal expansion aXl0+7 (Il-700 C.) +5. 8 +10. 8

In all of the work set forth in the foregoing tables, five rods were drawn from each melt and the dimensional stability measurements are based on the average stability of the ve rods. For the modulus of rupture tests, ten rods were drawn from each melt and the strengths set forth in the tables is the average strength of the ten rods. The modulus of rupture tests were performed on a Dillon Universal Tester, Low 'Range Head, having a 4 point loading with a support span of 4 inches and a loading span of 3A inch. The rods were each 51/2 inches in length and the loading rate adjusted so that the samples broke between 36 and 48 seconds. The l0 samples were abraded by tumbling for 15 minutes in a ball mill jar rotating at 75 r.p.m. and containing 250 grams of 240 grit SiC.

Compositions 23-35 and 59-66, inclusive, referred to m the above tables have the following compositions expressed in weight percents:

TABLE XI Composition number.-- 24 23 25 20 27 2s 29 30 31 32 33 34 35 59 e0 e1 62 53 04 e5 03 While glass-ceramics having high stability when exposed to temperatures as high as 1900" F. over extended periods of time are made from the SiO2-Al2O3-Li20 compositions of the first embodiment of the present invention, and while glass-ceramics having greater strengths are produced by the SiOZ-AlgOs-LizO-Zn() compositions of the second embodiment of the invention, many of the latter compositions do not produce glass-ceramics which are thermally stable at the 1900 F. temperatures. However, a small group of compositions containing Z110 and coming within the second embodiment of the invention, do have the requisite thermal stability at 1900 F. over a long period of time. Such compositions can be defined as having:

(1) a S102/ A1203 molar ratio of 5-8,

(2) a U20/A1203 molar ratio of 055-075, (3) a ZnO/LiO molar ratio of 0.04-0.5, and (4) a ZnO-l-LizO/Al203 molar ratio: S1, or

(l) a S102/ A1203 molar ratio of 4 to less than 5, (2) a U20/A1203 molar ratio of 0.55-0.75,

(3) a ZnO/Li2O molar ratio of 0.06-'0.5, and (4) a ZnO -i-LiZO/ A1203 molar ratio S1.

Compositions coming within these critical ratios and having good thermal stability at 1900J F. are Nos.: 39, 48, 49, 51, 53 and 56.

A matrix for a regenerative heat exchanger as disclosed in the aforementioned U.S. application Ser. No. 30,859 was made utilizing Composition 37 of the present invention. Such a matrix, broadly speaking, comprises integrally fused tubes forming a series of smooth longitudinal parallel passageways therethrough wherein the Walls dening the passageways have (1) essentially zero porosity, (2) consist essentially of an inorganic crystalline oxide material, (3) a maximum diameter of 0.1 inch, (4) a maximum thickness of about 0.03 to 0.002 inch through portions of the walls common to adjacent fused tubes, with the ratio of the diameter to such thickness being at least 3. The matrix has an open frontal area of at least 60% and the walls of the matrix have a thermal conductivity of less than 0.01 cal./cm./sec./cm.2/ C. at 400 C.

Glass tubing made from Composition 37 above and having an inner diameter of .030 inches and a Wall thickness of .0015 inches was cut into lengths 31/2 inches long and each end was sealed, trapping air therein.

The sealed tubing was tightly packed parallel to the length of a mold line with a layer of heat-resistant alumina-silica paper. The tubes within the mold were in a closely-packed parallel relationship with each other. The assembly was then heated in a kiln on the following schedule:

Temperature: Time or rate Ambient to 1250 F. 300 F./hr. Hold at 12.50 F. S hrs.

1250" F. to 2100a F. F./hr. Hold at 2100* F. 2 hrs.

2100 F. to room temperature 300 F./hr.

After this heat treatment, the resulting glass-ceramic matrix was removed from the mold and the ends of the tubes opened by grinding. The foregoing heat treatment thermally in situ crystallized the glass and produced a glass-ceramic matrix. The heat treatment had fusion bonded the walls of each tube to those of adjacent tubes and reformed each tube to substantially hexagonal shape. The matrix was suitable as a heat regenerator for a gas turbine engine, able to withstand the operating temperature of at least l500 F. for an extended period of time without any deleterious thermal instability occuring.

The above glass tubing of Composition 37 is also suitable for making the glass-ceramic recuperator matrix disclosed in U.S. application Ser. No. 30,859 and in the U.S. application Ser. No. 146,665, tiled May 25, 1971, as a divisional and continuation-in-part thereof. There, a plurality of layers of tubes are superimposed one above the other in successive parallel planes, the tubes Within each plane being essentially parallel to each other and transverse to tubes in adjacent layers. When subject to the same heat schedule described above with respect to the regenerator matrix, each tube becomes integrally fused to each adjacent parallel tube and each adjacent transverse tube. When, as preferred, the tubes are essentially fully expanded, each tube wall is a common wall with each tube adjacent thereto, including those in the same plane and those in adjacent parallel planes.

Moreover, when fully expanded, the passageways are essentially in the shape of a parallelogram, usually a square or a rectangle. After the heat treatment and the subsequent opening of the sealed ends, such as by grinding, an integral glass-ceramic recuperator matrix is obtained.

Using glass tubing formed from the compositions of the present invention, such as Composition 37, a core assembly for a thermal reactor for receiving the flow of hot gas effluents from a combustion engine, such as that disclosed in the aforementioned Zmuda et al. U.S. application tiled Mar. 23, 1971 can be made.

Such glass tubing is tightly packed together about a tubular member in parallel relationship, with each end of the tubing being sealed. The outer periphery of the assembly isv then constrained from outward movement in a direction perpendicular to the longitudinal passageways formed by the tubing and the tubular member. The assembly is then subjected to a heat schedule such that the tubing becomes softened and the air entrapped therein expands and urges the tubes into tight contact with adjacent tubes. A glass-ceramic matrix comprising a plurality of expanded tubes fusion-bonded together and to the tubular member is thus formed. The sealed ends of the tubing are opened and the matrix can then be utilized 17 in the manner disclosed in the aforesaid Zmuda et al. application to make the thermal reactor for a combustion engine.

What is claimed is:

1. In a recuperator matrix comprising an assembly of integrally fused tubes arranged in a plurality of layers of tubes superimposed one above the other in successive parallel planes, the tubes within each plane being essentially parallel to each other and transverse to the tubes in adjacent layers, the tubes in each layer forming a series of longitudinal parallel passageways through the matrix, wherein the walls of said passageways 1) have essentially zero porosity, and

(2) consist essentially of an inorganic crystalline oxide ceramic material, and wherein the inner diameter of said passageways is at least 3 times the Wall thickness through portions of said walls common to adjacent fused tubes, wherein the open frontal or cross-sectional area of each face of the matrix containing passageways is at least 32 percent of the crosssectional area across such face,

the improvement whereby such recuperator matrix can withstand temperatures of l500 F. for at least 1000 hours and said matrix will have a dimensional stability of less than 250 p.p.m. and will retain its strength, comprising having said inorganic crystalline oxide ceramic material of said matrix consist essentially of the glass-ceramic formed by thermally in situ crystallizing a glass consisting essentially of the following ingredients:

Ingredients: Weight percent SiO2 52-78.4 A1203 12.8-27.5 Li2O 2.4-7 ZnO 0.25-'6.'.7 Nucleating agent 3-9 Wherein said nucleating agent is selected from the group consisting of TiOz, ZrO2 and a mixture of TiO2 and ZrO2 and when said nucleating agent is TiO-z, it is present in an amount of at least 3.2 percent and when said nucleating agent is ZrOZ or the mixture, the ZrOZ is present in an amount not in excess of 3% by weight, wherein the ZnO+Li20/A1203 molar ratio is Sl, and wherein the SiO2/Al203 molar ratio is from 4 to 9 and (a) when the SiO2/Al203 molar ratio is from 4 t less than 5, the H2O/A1203 molar ratio is from 0.55 to 0.91, and the ZnO/LizO molar ratio is from 0.06 to 0.5;

(b) when the SiO2/Al203 molar ratio is from 5 to 8, the H2O/A1203 molar ratio is from 0.55 to 0.93, and the ZnO/Li-O molar ratio is from 0.04 to 0.5;

(c) when the SiO2/Al203 molar ratio is from more than 8 up to 9, the U20/A1203 molar ratio is from 0.8 to 0.93, and the ZnO/Li20 molar ratio is from 0.04 to 0.5; and

(d) the glass and resulting glass-ceramic contains in weight percent no more than 0.2 KZO, or 0.2 Na2O, or 0.2 (NagO-l-KZO),

said glass-ceramic having a coeficient of linear thermal expansion of -12 to .-i-l2 l0'Z (0- 700 C.). 2. In the matrix as defined in Claim 1 wherein said glass is selected from the group consisting of (A) a glass having (a) a SiO2/Al203 molar ratio of 5-8,

(b) a U20/A1203 molar ratio of 0.55 to 0.75,

(c) a ZnO/Li20 molar ratio of 0.04-O.5, and

(d) a ZnOI-i-LizO/Al203 molar ratio Sl; and

(B) a glass having (a) a SiO2/Al203 molar ratio of 4 to less than 5, (b) a U20/A1203 molar ratio of 0.55-0.75,

18 (c) a ZnO/Li20 molar ratio of 0.06-0.5, and (d) a ZnOH-Li2O/Al203 molar ratio S1, said glass-ceramic having a coeflicient of linear thermal expansion of --12 to l|12 l0'1 (0-700 C.).

3. In a matrix comprising integrally fused tubes forming a series of smooth longitudinal, parallel passageways therethrough, wherein the walls defining said passageways l) have essentially zero porosity, `(2) consist essentially of an inorganic crystalline oxide glass-ceramic, (3) and have a thermal conductivity at 400 C. of less than 0.01 cal./cm./sec./cm.2/ C., wherein the inner diameter of said passageways is at least 3 times the wall thickness through portions of said walls common t0 adjacent fused tubes and wherein the matrix has an open frontal cross-sectional area of at least 60 percent,

the improvement whereby such matrix can withstand temperatures of 1900 F. for at least 1000 hours and said matrix will have a dimensional stability of less than 250 p.p.m. and will retain its strength, comprising having said inorganic crystalline oxide ceramic material of said matrix consist essentally of the glass ceramic formed by thermally in situ crystallizing a glass consisting essentially of the following ingredients:

Ingredients: Weight percent 'SiOz 55-80 A1203 12-27 LigO 3.2-7.6 Nucleating agent 3-9 wherein said nucleating agent is selected from the group consisting of TiOg and a mixture of and when said nucleating agent is a mixture, the ZrOz should not exceed 3 weight percent, wherein the SiO2/Al203 molar ratio is from 4 to 10, and wherein (a) when the SiO2/Al203 molar ratio is from 4 to less than 5, the M20/A1203 molar ratio is from 0.75 to 0.97;

(b) when the Sig/A1203 molar ratio is from 5 to 7.5, the M20/A1203 molar ratio is from 0.65 to 0.97;

(c) when the Si2/Al2O-3 molar ratio is more than 7.5 and less than 9, the Li2/O/Al2O3 molar ratio is from 0.8 to 0.97;

(d) when the SiO2/Al203 molar ratio is more than 9 and up to 10, the M20/A1203 molar ratio is from 0.87 to 0.97,

said glass-ceramic article having a coefficient of linear thermal expansion of --12 to [-}-12 l0'1 (0-700 C.).

4. In a matrix comprising integrally fused tubes forming a series of smooth longitudinal, parallel passageways therethrough, wherein the walls defining sai-d passageways (1) have essentially zero porosity,

(2) consist essentially of an inorganic crystalline oxide glass-ceramic,

( 3) and have a thermal conductivity at 400 C. of less than 0.01 cal./cm./sec./cm.2/ C., wherein the inner diameter of said passageways is at least 3 times the wall thickness through por-tions of said walls common to adjacent fused tubes and wherein the matrix has an open frontal cross-sectional area of at least 60 percent,

the improvement whereby such matrix can withstand temperatures of 1500 F. for at least 1000 hours and said matrix will have a dimensional stability of less than 250 p.p.m. and will retain its strength, comprising having said inorganic crystalline oxide ceramic material of said matrix consist essentially of the glassceramic formed by thermally in situ crystallizing a wherein said nucleating agent is selected from the group consisting of TiO2, Zr02 and a mixture of Ti02 and ZrO2 and when said nucleating agent is Ti02, it is present in an amount of at least 3.2 percent and when said nucleating agent is ZrO2 or the mixture, the Zr02 is present in an amount not in excess of 3% by weight, wherein the molar ratioIk is S1, and wherein the SO2/A1203 molar L ratio is from 4 to 9 and (a) when the SO2/A1203 molar ratio is from 4 to less than 5, the H2O/A1203 molar ratio is yfrom 0.55 to 0.91, and the ZnO/Li20 molar ratio is from 0.06 to 0.5;

(b) when the SiO2/Al203 molar ratio is from 5 to 8, the U20/A1203 molar ratio is tlrom 0.55 to 0.93, and the ZnO/Liz'O molar ratio is from 0.04 to 0.5;

(c) when the SO2/.A1203 molar ratio is from more than 8 up to 9, the H2O/A1203 molar ratio is from 0.8 to 0.93, and the ZnO/Li2O molar ratio is from 0.04 to 0.5; and y(d) the glass and resulting glass-ceramic contains in weight percent no more than 0.2 K2O, or

0.2 N320, r 0.2 (NagOH-Kgo), said Iglass-ceramic having a coecient of linear thermal expansion of v 1?. to }-12 l0'7 (0- 700 C.). 5. In a matrix of Claim 4, the improvement wherein said glass is selected from the group consisting of (A) a glass having (a) a SO2/A1203 molar ratio of 5 8, (b) a lH2O/A1203 molar ratio of 0.55 to 0.75, (c) a ZnO/LizO molar ratio of 0.04-0.5, and (d) a ZnO-l-LizO/A12O3 molar ratio g1; and a glass having (a) a SiOz/AIZOS molar ratio of 4 to less than 5, (b) a U/A1203 molar ratio of 0.55-0.75, (c) a ZnO-/LizO molar ratio of 0.06-0.5, and (d) a ZnO-l-LiZO/AlgO'a molar ratio S1, said glass-ceramic having a coefficient of linear thermal expansion of -12 to |12 10'7 (ll-700 C.). 6. In a matrix comprising an assembly of integrally fused tubes arranged in a plurality of layers of tubes superimposed one above the other in successive parallel planes, the tubes within each plane being essentially parallel to each other and transverse to the tubes in adjacent layers, the tubes in each layer forming a series of longitudinal parallel passageway/s through the matrix, Where.

in the walls of said passageways `(1) have essentially zero porosity, and

Cil

(2) consist essentially of an inorganic crystalline oxide ceramic material, and

wherein the inner diameter of said passageways is at least 3 times the wall thickness through portions of said walls common to adjacent fused tubes, and wherein the open frontal or cross-sectional area of each face of the matrix containing passageways is at least 32 percent of the crosssectional area across such face,

the improvement whereby such matrix can withstand temperatures of 1900D F. for at least 1000 hours and said matrix will have a dimensional stability of less than 250 ppm. and will retain its strength, comprising having said inorganic crystalline oxide ceramic material vof said matrix consist essentially of the glass-ceramic formed by thermally in situ crysstallizing a glass consisting essentially of the following ingredients:

Ingredients: Weight percent SiO2 55-80 A1203 12-27 Li-O 3.2-7.6 Nucleating agent 3-9 wherein said nucleating agent is selected from the group consisting of TiO2 and a mixture of and when said nucleating agent is a mixture, the Zr02 should not exceed 3 weight percent, wherein the SO2/A1203 molar ratio is from 4 to 10, and wherein (a) when the SO2/A1203 molar ratio is from 4 to less than 5, the U20/A1203 molar ratio is from 0.75 to 0.97;

(b) when the SiO2/Al203 molar ratio is from 5 to 7.5, the yU20/A1203 molar ratio is from 0.65 to 0.97;

(c) when the SiO2/A12O3 molar ratio is more than 7.5 and less than 9, the U20/A1203 molar ratio is from 0.8 to 0.97; and

(d) when the SO2/A1203 molar ratio is more than 9 and up to l0, the LigO/AlZOa molar ratio is from 0.87 to 0.97,

said glass-ceramic article having a coecient of linear thermal expansion of -12 to l-l2 10-'I (0-700 C.).

References Cited UNITED STATES PATENTS 3,157,522 11/1964 Stookey 106-39.7 3,112,184 11/1963 Hoilen-bach 25--156 3,573,150 3/1971 Broutman et al. 161-55 3,279,931 10/ 1966 -Olcott 106-39 3,251,403 5/ 1966 Smith 165-10 3,325,266 6/1967 Strong 65-33 3,502,596 3/1970 :Sowards 252-477 GEORGE F. LESMES, Primary Examiner W. R. DIXON, JR., Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION 0 PATENT No. 3,8Lr1,95o

DATED October 15, 19'7Lr |NVENTOR(S) Jerry L. Planchock, Thomas W. Brock, Daniel R. Stewart It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 67, change "not" to now Col. 3, line 73, delete "0.87 to 0.97; and when" and insert therefor Twenty-sixth Da)l of october 1976 O [SEAL] RUTH C. MASON C. MARSHALL DANN e Atlesting Officer Commissioner nfPalenls am! Trademarks 

1. IN A RECUPERATOR MATRIX COMPRISING AN ASSEMBLY OF INTEGRALLY FUSED TUBES ARRANGED IN A PLURALITY OF LAYERS OF TUBES SUPERIMPOSED ONE ABOVE THE OTHER IN SUCCESSIVE PARALLEL PLANES, THE TUBES WITHIN EACH PLANE BEING ESSENTIALLY PARALLEL TO EACH OTHER AND TRANSVERSE TO THE TUBES IN ADJACENT LAYERS, THE TUBES IN EACH LAYER FORMING A SERIES OF LONGITUDINAL PARALLEL PASSAGEWAYS THROUGH THE MATRIX, WHEREIN THE WALLS OF SAID PASSAGEWAYS (1) HAVE ESSENTIALLY ZERO POROSITY, AND (2) CONSIST ESSENTIALLY OF AN INORGANIC CRYSTALLINE OXIDE CERAMIC MATERIAL, AND WHEREIN THE INNER DIAMETER OF SAID PASSAGEWAYS IS AT LEAST 3 TIMES THE WALL THICKNESS THROUGH PORTIONS OF SAID WALLS COMMON TO ADJACENT FUSED TUBES, WHEREIN THE OPEN FRONTAL OR CROSS-SECTIONAL AREA OF EACH FACE OF THE MATRIX CONTAINING PASSAGEWAYS IS AT LEAST 32 PERCENT OF THE CROSSSECTIONAL AREA ACROSS SUCH FACE, THE IMPROVEMENT WHEREBY SUCH RECUPERATOR MATRIX CAN WITHSTAND TEMPERATURES OF 1500*F. FOR AT LEAST 1000 HOURS AND SAID MATRIX WILL HAVE A DIMENSIONAL STABILITY OF LESS THAN 250 P.P.M. AND WILL RETAIN ITS STRENGTH, COMPRISING HAVING SAID INORGANIC CRYSTALLINE OXIDE CERAMIC MATERIAL OF SAID MATRIX CONSIST ESSENTIALLY OF THE GLASS-CERAMIC FORMED BY THERMALLY IN SITU CRYSTALLIZING A GLASS CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS: 